It is commonly known that the Amazon rainforest absorbs greenhouse gases – but scientists now draw attention to the mystery of the seafloor, where microbial communities eat up gigatons of methane
The seafloor is a mystery to many people, a place where it is ordinarily too dark for human eyes to perceive. Researchers on a routine survey recently found life, 900 metres below an Antarctic ice shelf. Deep in the dark and cold, a small community of stationary animals attached to boulders is thriving against the odds.
When it comes to the role of ice in the climate, the image of polar bears without adequate homes is common. But ice also holds carbon, which is being released into the air as ancient permafrosts thaw.
Now, scientists are looking at one of the most obscure creatures in the ocean – microbial communities, which are consuming more and more methane. Over the years, researchers are finding more methane beneath the seafloor, yet very little ever leaves the oceans and gets into the atmosphere. While the microbes are eating it up, where is the rest actually going?
Peter Girguis, Professor of Organismic and Evolutionary Biology, Harvard University, said: “The microbes in these carbonate rocks are acting like a methane bio filter consuming it all before it leaves the ocean.”
Why are seafloor carbonate rocks important?
Seafloor carbonate rocks are common, but in select locations, they form unusual chimney-like structures. These chimneys reach 12 to 60 inches in height and are found in groups along the seafloor resembling a stand of trees. Unlike many other types of rocks, these carbonate rocks are porous, creating channels that are home to a very dense community of methane-consuming microbes. In some cases, these microbes are found in much higher densities within the rocks than in the sediment.
Professor Girguis further said: “We measured the rate at which the microbes from the carbonates eat methane compared to microbes in sediment.
“We discovered the microbes living in the carbonates consume methane 50 times faster than microbes in the sediment. We often see that some sediment microbes from methane-rich mud volcanoes, for example, may be five to ten times faster at eating methane, but 50 times faster is a whole new thing. Moreover, these rates are among the highest, if not the highest, we’ve measured anywhere.”
A natural form of electrical current?
An intriguing revelation find was that some of these microbes are surrounded by pyrite, which is electrically conductive. One possible explanation for the high rates of methane consumption is that the pyrite provides an electrical conduit that passes electrons back and forth, allowing the microbes to have higher metabolic rates and consume methane quickly.
“These very high rates are facilitated by these carbonates which provide a framework for the microbes to grow,” said Professor Girguis.
“The system resembles a marketplace where carbonates allow a bunch of microbes to aggregate in one place and grow and exchange – in this case, exchange electrons – which allows for more methane consumption.
“Next we plan to disentangle how each of these different parts of the carbonates – the structure, electrical conductivity, fluid flow, and dense microbial community – make this possible. As of now, we don’t know the exact contribution of each.”